import java.util.Random;

public class Main {
    public static void main(String[] args) {
        char[] charArr = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k'};
        Random r = new Random();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 4; i++) {
            int index = r.nextInt(11);
            sb.append(charArr[index]);
        } String result = sb.toString();
        System.out.println("验证码:" + result);
        String string;
        //Integer.toString()
    }
}